basically PAO has two advantages:
- Less loci needed
- Grouping of information
the first is the main reason for a lot to switch to PAO, it allows for more information to be stored on one locus and thus you need less loci. Basically without PAO (or something similar) you can generally store 1, 2 or 3 digits on a single locus, with PAO that range goes from 3 to 9 digits, depending on how complex you want to make your system. I have yet to see a system allowing 10-digits with PAO, but that even would be possible. It is possible to extend your range by adding more complexity to the system, but PAO is an effective middle ground.
I hear a lot about PAO with totals of 8 digit images, 3-digit persons, 2-digit actions, 3-digit objects, because in memory competitions the numbers seem to come in 40-digit rows, which makes 8 a better option than 6 or 9 as you really work row by row. But that is basically what it is for, storing lots of information on a small spot.
The second is useful in real life. When I finish my milennium PAO with 8-digit images, I can use that perfectly for phone numbersl, especially mobile phone numbers. also birthdays and stuff like it can be remembered with it. By using PAO, I can put all that information in a single image. Even if you have to split it up, you only have to connect two images, which is easier than connecting five in a specific order.